1. Field of the Invention
The present invention relates to an active object detection sensor that transmits detection rays for object detection toward a detection area, and detects an object based on a reception signal generated when receiving detection rays reflected by the object.
2. Description of Related Art
To date, an active object detection sensor has been known which transmits detection rays, such as infrared rays or near infrared rays, for object detection, from a transmitter toward a detection area, causes a receiver that receives detection rays reflected by an object to generate a reception signal, and detects the object such as a human body when the reception signal is determined as having a level that exceeds a setting level.
As the active object detection sensor, the use is made of a sensor that forms a detection area divided into a plurality of division areas, to arrange plural columns of the division areas in a lateral direction, and arrange plural rows of the division areas in a longitudinal direction from a position close to the sensor toward a position distant from the sensor (for example, Japanese Laid-Open Patent Publication No. 2009-115792). The active object detection sensor is, for example, used for an automatic door sensor so as to detect an object for the automatic door.
FIG. 5A shows an example of a conventional sensor. The sensor 110 includes four phototransmitter (transmitter) elements 23 (elements EA to ED) and four photodetector (receiver) elements 24 (elements Ea to Ed), which are paired, respectively, so as to form four pairs, with lens bodies 25, 26 provided for between the phototransmitter elements 23 and the photodetector elements 24. For example, a light transmission area (transmission area) TA by the element EA and a light reception area (reception area) RA by the element Ea are overlaid or overlapped on each other to form a division area A1 of a first row or line, and a light transmission area TA by the element EB and a light reception area RA by the element Eb are overlaid or overlapped on each other to form a division area A2 of a second line. As shown in FIG. 5B, a detection area AA is formed by the four lines of the division areas A1 to A4, which lines are arranged in the longitudinal direction, from a position close to the sensor 110 toward a position distant from the sensor 110. In the example described herein, the division area A1 of the detection area AA is formed by combination of the element EA of the phototransmitter element 23 and the element Ea of the photodetector element 24, and the division area A2 is similarly formed by combination of the element EB and the element Eb. Thus, the respective combination of the phototransmitter element and the photodetector element which form each division area is different from a combination of the phototransmitter element and the photodetector element which form another division area, such that each combination is individually unique (hereinafter, referred to as a one-to-one relationship) and the same combination is not formed, thereby enabling each of the division areas A1 to A4 of the detection area AA to be uniquely identified. It is to be noted that a plurality of division areas are similarly formed in the lateral direction for each of the four lines of the division areas A1 to A4, which lateral division areas are not shown.
In order to improve safety and starting performance of an automatic door, intervals between the division areas need to be maintained constant while the detection area is extended in the longitudinal direction. Therefore, it is considered that the number of the phototransmitter elements and the photodetector elements are increased. FIG. 6A shows a sensor 120 in which the phototransmitter elements 33 and the photodetector elements 34 are paired respectively so as to form six pairs, that is, additionally including two pairs of the phototransmitter element 33 and the photodetector element 34 as compared to the sensor shown in FIG. 5A. As shown in FIG. 6B, the detection area AA having six rows or lines is formed by the six rows or lines of division areas A1 to A6 disposed in the longitudinal direction, from a position close to the sensor 120 toward a position distant from the sensor 120. Also in this example, combinations between the phototransmitter elements 33 (elements EA to EF) and the corresponding photodetector elements 34 (elements Ea to Ef) are provided in the one-to-one relationship, and each of the division areas A1 to A6 of the detection area AA can be uniquely identified.
However, in a case where the number of the transmitter elements and the receiver elements is increased, cost is increased correspondingly. Further, increase of the number of elements causes increase of the size of a device, and associated components need to be added, thereby further increasing cost.
It is known that, for addressing the above problem, a prism is disposed in front of the elements and the lens body to extend the detection area while the number of elements is reduced (for example, Japanese Laid-Open Patent Publication No. 2013-50368). In a sensor 130, as shown in FIG. 7, in a case where a prism is used, a detection ray transmitted from an element EA of a phototransmitter element 43 is divided in two directions by two prism surfaces of a prism 47, to form an area A and an area A′ of a light transmission area (transmission area) TA, and a detection ray to be received by an element Ea of a photodetector element 44 is incident on a prism 48 from two directions from the area a and the area a′ formed in a light reception area (reception area) RA, and the rays from the two directions are each transmitted toward the element Ea by two prism surfaces of the prism 48. For example, a first line is formed by the area A of the light transmission area TA and the area a of the light reception area RA, and a fourth is formed by the area A′ of the light transmission area TA and the area a′ of the light reception area RA, to form division areas A1 and A4 respectively. At this time, the area A and the area A′, in the light transmission area TA, by the element EA of the phototransmitter element 43 cannot be distinguished from each other, and the area a and the area a′, in the light reception area RA, by the element Ea of the photodetector element 44 cannot be distinguished from each other. Therefore, the division areas A1 of the first and A4 of the fourth are determined as the same area. The second and the fifth are similarly determined as being the same, and the third and the sixth are similarly determined as being the same. In a case where the aforementioned prism is used, the combination of the phototransmitter element 43 and the photodetector element 44 in each division area does not satisfy the one-to-one relationship, and the detection area cannot be uniquely identified.